The present invention relates to electromagnetic signal receiving systems, and more particularly to a receiving system wherein the polarization of the receive antenna is matched to that of the incoming RF signal, thereby maximizing the received signal-to-noise ratio.
In many instances, the polarization of the receive signals is not known or may vary due to ionospheric attenuation and reflection, multipath interference or geometric relationship between the source and the receiving antenna. In certain instances, it is possible that the polarization of the signal at the source may be varying for one reason or another.
Generally, the polarization of the receive antenna is made to match to that of the incoming signal. However, when the polarization of the receive signal is not known or tends to change, a polarization diverse antenna is generally used. This type of antenna receives either two orthogonal linearly or circularly polarized signals. For the maximum reception of the incoming signal, these two orthogonally polarized components must be matched in relative phase and amplitude to that of the incoming signal. If only one component is used, which is generally the case, no signal may be received if the received signal polarization is orthogonal.
It is well known that any receive signal can be decomposed into two linear components with certain relative phase. In other words, a complete polarization match can be made by adjusting the relative phase and amplitudes of the two orthogonal linearly polarized signals. Schemes for matching the incoming polarization have been considered for high performance space communication systems where signal levels from deep space probes are often very marginal. These schemes primarily have used mechanical polarization adjustment systems. Although not directly related, polarization mismatching schemes are used for adaptive nulling of the jammer signals. However, none of these schemes require the polarization to be matched in very short time without losing any information, that is, from pulse to pulse.